The pitfalls of overlooking correctable causes of progressive intellectual deterioration are illustrated by live patients whose conditions were originally diagnosed as primary dementia. In each case careful evaluation disclosed a reversible process. Treatable intracranial conditions, systemic illnesses, endocrinopathies, deficiency states, collagen-vascular disorders, heavy-metal intoxications, exposure to industrial agents, infections, and the effects of drugs must all be considered in the evaluation of the patient with dementia. Such conditions are less likely to go undiagnosed when dementia is regarded as a nonspecific syndrome of progressive intellectual compromise rather than a specific diagnosis.